andres



Aug. 11, 1959 R. K. ANDRES AUTOMATIC SWITCI-IING CIRCUIT 2 Sheets-Sheet l Filed Feb. 24, 1955 .du me m H N N@ N QN uw v. m k lLrJL Q: Nw B w+ @5w m w NN N S W N ...im w m w k QW N fr@ RN ww, l@ x .lslwh w www I w. 9 m l@ A @wm V9 n hwm Q x N. 9 k mw Novww Aug. 11, 1959 Filed Feb. 24, 1955 R. K. ANDRES AUTOMATIC SWITCI-IING CIRCUIT 2 Sheets-Sheet 2 kmwmnwms FER 7/0 2,899,497" .l Patented Aug. 11b, :19.59:

p 2,899,497 AUTOMATIC' swrrcHiNo' einem K. Andres, Glen Cove, l N.Y.,. assigner lto Radio Cofi poration of America,racorporationof- Delaware xppli'csfiunrebmry/za; tasa-serial No. 490,175;

' commis-tcl.117,8--17i` -V mechanism. Automatic switchingcircuits'have.been dei vised', which are responsive to. such acontrol signal,. to act as a director for .switchingzsuch a control'vsignal among a plurality of telegraphltransmitters. Thecontrol signal may be a continuous potentialsignal ,when the transmitters are' operating. solo or inl single signal: condition..l .In recent years, howeven'the multiplexI operation of telegraph transmitters. has/found wide acceptance, muchof telegraph communication now being:4 carried out in -this form of transmission.. In addition, synchronous multiplex operation readily lends itselito error vdetection andffautomatic error correctionisystems of. the return channel rte-cyclingv type. I A l .v f

Automatic switchingcircuits have been constructed which, are suitable for use with; the continuous'rpotential type of transmitter controlv signal. This type of control signal, however, cannot be used with the multiplex type ofv operation, because it is necessary to supply the control signal in a pulse formto synchronously operate a multiplex transmitter arrangement. A switching circuit suitable for use with a continuous potentiall controlled transmitter is not suitable for use with a'pulse controlled multiplex transmitter due to the fact that in multiplex operation it is essential that the switching circuit act as both director and synchronizer. of the .control pulsepto insure the synchronized operation of the telegraph transmitter. It has,j therefore, been necessary toI maintain different automatic switching circuits for both types of transmission, namely, multiplexandnon-multiplex transmitter operation. Attempts todevise switching circuits suitable for use with both types of operation have resulted in' complicated circuitry and arrangementsy including an excessive number of componentsv anda manual' operation` to switch from. one type of operation to the other.

For reasons of economy and ease of operation, it is necessary that a transmitting station be equipped with an` automatic switching circuit which will beY responsive to both types of control signals. Such. an `automatic switching circuit should be able to control the operation of a multiple number of transmitters in response to either a continuous type of control signal or a pulse or multiplex type of control signal.

.y lIt is an object of the invention toI obtain an improved automatic switching circuit for multiple telegraphtransmittel' control. .r f. Y

Itis a further objectief theinvention to obtain a novel form of automatic switching; circuit responsive to either a continuous potential control signal orY pulse type of control signal for mul'tipletelegraph transmitter control.

It-'is a still further object of the inventionzto obtain an automatic switching circuit whichfmayf interchangeably beutilized to` controlthe operation of. a. multiple number ofv'multiplexoperated telegraph transmitters or a multiple number of nonmultiplex operated telegraph transmitters.

. It is a .stillfurther object oftheinventibn,` to obtainsan automatic switching circuit( for; multiple telegraph transmitter control which issimple and: compact in construction. l f

The objectslof theinvention: are accomplished@ by a switching circuiti includingt anumber.l of multiple; Contact relays. Y. The contacts and windings ofQthefrelays: aref'interconnected' in .such a manner that, wheny aVV particular telegraph transmitter is selected for operation, vthe relays are activated ande. deactivated inV a predetermined sequence to connectacontroly signalto successiveindividual transmitters; of a group, ina1predetermined=sequence. The sequence-,ofcperationfia in turn controlled by one ofi the relays which isresponsivetoa control signal; l

When ther transmittersgarea operating solo o'rin a single signal condition (as distinguished'from multiplexvoperaftion), the circuit will operi-atefmuch as' any other switch ing; circ,uit-,. acting? as:v an? on-off: controlv for distributing the cont-rolsignal. to anumber. cdtransmitters." However, whenfthe'circuitiisto befzused withfa vnumberotiY transmitters-which are to be: used inf. multiplex operation,- certain allowances must: bemade' in thercircuit. The switchingcircuit', in: order' toi satisfactorily control the operation of a-Lgroup of. transmittersfin synchronismwith the multiplexing. equipment-,'.must insurea that the' c ontrolfY signal pulseis synchronouslyf switched as.' ai completepulse'fo the individual:transrifiittei'sI of'ther group and in accordance with` thel predeterminedzsequence; i The control' signal from themultiplexing equipmentis' in. thefform? of pulses' of suitablexamplitude and. 'durationto control the trasmitter. ,If the switching circuit should switch thecom trol pulse line to. any` 'onecf the multiple transmitters withoutb'eing synchronizediwith the arrival of the'"cone` trol ypulsev .froni ,the multiplexing equipment, the' liist characters of'asr'nessage transmitted from the Vmultiplexing equipment will he mutilatedl and: considerabley diliiculty will bev experienced in: `communicating'a clear and: correct message,tosa;distantjpoint;I I' f "f To achieve' the interchange'blenatuie; of the switching circuit, that is, one thats capable" of`-usewitheither ai multiplexer. non-multiplex form of transmission, the' lrelay which'controls the''synclir'oznizing function and thus theseq'uential timing ofthe' circuit is'. in one embodiment aslow operate-slow release typeLf Such a relay serves. yto properly'` control: transmitters which ,may bel multiplex or non-multiplex `in operation, ;and rdoes not deleteriously. affect the Opration of `dief-circuit.itfa continuous or steady battery c'ont'r'olf signal for. non-rnultiplexr.operationtis uti@` liz'edl On the other hand,.the circuiti automatically-Lelirn#4 inates therandormtimingibetween theinitiation ovf 'the message andthe arrivall ofthejcontrol pulse', from `the` multiplexing' equipment whentheA transmitters are beingV y Operated in afrelaxationtcontrol mannerirom' an elec? troni'cormcchanicalfmultiplex. The relaycircuit insures thatl only completefcontrol-pulsesfwillbe passed to the clutch magneti o'am'essage transmitter by'A counting-the ii'rst` completecontrollpulse er fraction-thereof and utili" j ing; thisirst'f control pulse :to-'complete' the Balance of the* switching functions, thereby, avoiding the mutilation of the first characters of a message as would occur if the switching circuit were not in synchronism with the transmitting multiplex equipment.

Typical telegraph transmitting stations include an auxiliary transmitter which is automatically used to transmit a message before the regular message transmitter is permitted to-proceed. Such -an auxiliary trans- ,mitter may transmit routing information and/or one of a sequential group of numbers, thereby, directing the message to a particular. destination and/or numerically identifying the` subsequent message. Such an auxiliary transmitter, as in the case of the regular message transmitter, must be controlled so that proper operation will result when either multiplex or non-multiplex operation is used. The automatic switching vcircuit of the inventionincludes the automatic control of such an auxiliary vtransmitter and insures its proper operation regardless of the type of operation utilized? A more detailed description of the invention follows with reference to the accompanying drawing in which:

Figurel discloses an automatic switching circuit, constructed in accordance with the invention, for controlling the operation of a pair of message telegraph transmitters and an auxiliary transmitter;

Figure 2 is a chart given in explanation of the con- -nections to the terminals 1 to 9 shown in Figure 1;

Figure 3 is a chart of the make-up of a particular set of relays suitable for use in the circuit shown in Fig. l and is given only by way of example; and

i Figure 4 is a schematic drawing of the particular relays included in Fig. 1 and Ydescribed in Fig. 3 disclosing the construction of the contacts thereof.

Referring to Figures 1 and 2, there is shown an automatic switching circuit for automatically controlling the operation of a pair 4of message telegraphv transmitters A and B and an auxiliary transmitter N. These transmitters are shown in box form at the left of Fig. 1 and may be any suitable clutch controlled telegraph transmitter type using sensing pins in association with a multi-element punched tape for sending out a multi-element code signal such as a S-unit signal, for example. Theauxiliary transmitter N will, for purposes of description, be referred to as a numbering transmitter, but it is to be understood that the transmitter could be utilized to automatically transmit any form of information desired. The intelligence carrying output circuits of the transmitters A, B and N are connected to utilization circuits, not shown. The outputs' of the transmitters may be connected to a commoncircuit keying multiplexing equipment or directly keying a radio frequency transmitter. the transmitters are fed will depend upon the method of operation of the communication 'system within which the transmitter and automatic switching circuit of the invention are to be'employed.

When it is desired to transmit a message, one of the telegraph message transmitters A or B is selected for use. It will be assumed, hereafter, that transmitter A has been so selected, but it is to be understood that the operation of the circuit upon the selection of transmitter B will be the same. example, is inserted in transmitter A closing the automatic stop contacts of transmitter A and completing a ground circuit thru terminal 6, lead 30, the winding of relay FA, armature 9 and contact 8 of relay FB, lead 31, and resistor R3 to the positive or plus terminal of a source of potential. Relay FA will then operate. Upon the operation of relay FA, contact 8 and armature 9 of the relay FA will openand open the circuit thru thewinding of relayFB, which is connected on one side to transmitter B thru lead 32 and terminal 7, and on the other side to the positive terminal of a. source of potential thru the Yforegoing contacts. energization of relay FA prevents Vthe operation of trans- The The particular circuit to which the outputs of mitter B by the switching circuit while transmitter A is in operation. Stated otherwise, the switching circuit of the invention permits a control signal to be applied either to transmitter A or transmitter B but not to both transmitters at the same time, as will appear hereinafter. Relay FB is locked out by'the operation of relay FA. The operation of relay FA closes a circuit to operate relay A over a path traced from the positive terminal thru resistors R1 and R2, make Contact 1 and armature 2 of relay FA, resistor R4 and the winding of relay A to ground thru armature 9 and break contact 8 of relay E and armature 9 and beak contact 8 of relay C. Two shunt-connected resistors R1 and R2 are used in the embodiment shown in Fig. 1 to permit proper power dissipation. However, resistors R1 and R2 may be replaced by a single resistor in a particular application without Vdeparting from the spirit of the invention. When relay A operates, a control signal, which may be a multiplex control pulse or a continuous potential signal, as will be more fully discussed later, supplied to terminal 1, passes. thru resistor R5, armature 9 and make contact 10 of relay A, resistor R6 and thru the winding of relay B to ground, operating relay B.

When relay B operates, a circuit is closed to operate relayC over a path traced from the positive terminals throughresistors R1 and R2, make contact 1 and armature2 of relay FA, lead 33, armature 2 and make contact 3 of relay B, break contact 3 and armature 4 of relay D, resistor R7 and thru the winding of relay C, operating relay C which completes its ground circuit via lead 37 and terminal 3 and the normally closed letters contacts of the numbering transmitter N. Upon the operation of relay C, break contact 8 will no longer engage armature 9 of relay C, thereby, breaking the ground connection to the winding of relay A and interrupting the operating circuit thereof, releasing relay A. The positive terminal of a source of potential is then connected thru resistor R9, armature 2 and make contact 1 of relay C, lead 38 and resistor R7 to the winding of relay C, causing relay C to self-hold. Upon the operation of relay C, a circuit is closed to operate relay D over a path traced from the positive terminal thru resistor R8, armature 7 and make contact 6 of relay C to ground thru resistor R10 and the winding of relay D. Relay D will hold itself operated by a circuit traced from the winding of relay D through resistor R10, make contact 10 and armature 9 of relay D, lead 33, armature 2 and make contact 1 of relay FA and resistors R1 and R2 to the positive terminal of a source of potential. At this point, the control signal appearing at terminal 1 having previously activated relay B, which is now deactivated dueto the deactivation of relay A by the opv eration of relay C, will pass thru armature 9 and break i signal will start a number tape or other means for trans` The message, if on tape, for

mitting one of a' sequential group of numbers. After the numbering transmitter has completed the transmission of a number, the letters combination sensed following the number upon the tape, if a tape is used, opens the automatic stop contacts of the numbering transmitter connected to terminal 3, thereby, removing the ground from terminal 3 and the winding of relay C, releasing relay C. n

When relay C releases, the ground connection is rer stored to the winding of relay A thru break contact 8 and armature 9 of relay C and break contact 8 and armature 9 ofrelay E, operating relay A. When relay A 1s operated, as described above, make contact 10 engages armature 9 of relay A connecting a signal appearpulse.

was previously the` case, due to the fact that theoperating circuit for relay Cv is opened by ther-activation of relay D which disengages armature 4 of relay D from itsI break contact 3, thereby disconnecting the winding of. relay C Vfrom the positive terminal. Relay C cannot operate at this time. 4When relay B operates, a circuit is closed to operate relay E over a path traced `froml the positive terminal thru armature 2 and, make contact 1- of relay lfA, lead 33, armature 2' and make contact 3` of= relay B, lead 35, and resistor R11 to the winding.v of relay E which is connected to ground thruilead 36,arma5 turc 9 and break contact 8 of relay C. Relay Ey will self-holdby amcircuit traced from y the positive terminal thrux resistorA R12, make contact 6 and armature7 of relay E, make Contact o sand'armature 7 of relay D` and resistor R11. In addition, the opening of break contact 8 and armaturel 9 or'r'elayfE, upon tli'e1 operation of' relay E, releases relay A bydisconnecting: the ground connection to the winding off the relay.A Thevdeactivation offrelay'A, in turn', releasesrelay B via the disengagement of make contact )V and armature 9` ofy relay= which' disconnects terminal 1 from the' winding of relay B.

t ttiisp'oint, the control signal on terminal I passes' thru' resistor' R5, armature 9 and contact 8i of relay A, lead 34; contact 9` and armature 8 o'f relay' B, armature 4`i and Contact 3l ofv relay C, armature) 2 and contact 1i' of relay E, contact 1- and armature 2v of relay D and armature 7 and Contact Gf ofrelay to terminal 4V whichv isfconnected'to the clutch magnet of message'tra'nsmitter A, thereby operating transmitter A. When ames# sage has passed completely thru the message' transmitter A, the automatic stop contacts of AA transmitter, which are connected to terminal 6, will beT opened removing ground` from the winding of relay FA, releasing relay FA. When relay FA` releases, relays D and E which are activated will also be released The disengagement of' contact 1I and armature' 2 of relay FA- disconnects the positive terminal from the winding' of relay D'. Contact 6'; andi armature 7 vof rel'a'y'Dwill open disconnecting the positive terminali from the winding ofv relay E; The entire switching sequence is'deactivated, and? is ready for immediate use upon the grounding of either terminal 6 or 7 which are connected to transmitters A and B, respectively, one ofwhich may' now' be selected or" have" already been selected for further operation.

Anl importantl aspect of the invention isv the fact that the"` automatic switching' circuit will operate toVv controll the'A selection ,of a transmitter in response to either a continuous potential control signal or multiplex control The foregoing descriptionl outlines the operation of' the circuit when a continuous or steady battery controlsignalistbeing received at terminal' 1. Such a signal could be supplied from astandardk battery or anyftype of generator capable of 'delivering' a* steadyY continuous potential signal. The circuit`wi1l operate' to automatically connect terminal 1 to the numbering transmitter andg-therea'fter, to one'- of the' message'transmitters A- or B2 that has been' selected for operation. In order to permitV the: operation of the circuit in" connection withfmulti'- p'leX` equipment, it' is necessary to supply control pulses at" terminal' 1'r which' will operate the'l switching' circuitl andi thus the message or. numberingftransmitters'- ini syn`- chronism with the multiplex transmitting; equipment. TheV control pulses may be supplied from the multiplex equipmentor from apulse generaton; theA operation ofv which is controlled by the multiplexf equipment. When' an operator connects terminals' 6 or '7 to ground by selecting the transmitter lne-wishes to operate-,he has no' way4 ofV knowing when a synchronizing` pulse. willappear atterminal 1. If the circuit` were allowed to operate merelyv as a distributing device forv the control pulse,.- the` switching functions. wouldV beY completed. at random with respect to'the arrival of the rst control. pulse, thereby connecting thel controlv pulse line, terminal. 1 to the transmitter` clutch. magnetr at random. This is` obJcctionable inthat` an incomplete ,controll pulse could be. passed to'the clutch ofy the numbertransmitter' thru-f4 terminal 2 ormessageV transmitters thru terminals 4 and- 5. The transmitters would be placed in operation` outy of synchronism with the controlA pulseutilized infthe. multiplex operation. The rst few characters of the multiplex mes-v sage transmittedV would' therefore be mutilated causing considerable delay and diliiculty in completing` the trans. mission ofa-message to a distantv location. l y, Y.

To avoid this diiiiculty, relay `B` is4 in one embodiment a slow operate-slow release type whosetotal operating cycle in conjunction with relays C and Dpissuficient to insure the counting'of the irst complete controla pulse or sutiicient part thereofV and to' have completed the switching functions of therelays so that theA next. conrplete control pulse canpass tothe clutch-of the` number transmitterv N thru terminal 2 or message-,transmitters Aand B thru terminals 4 or 5.--V Ituatithe time the-con-V tacts of.v relay complete a.- circuit to the winding off relay B from terminalAv 1'Y a pulse of. insuiicient remaining duration was being received at terminal. 1;. relay B,. because of its slow operate characteristics,. would not become activated. Immediately, however, upon the reception of the next control pulse, relay B will'loperate. Contact 3v and armature 2 of relay Bi activating relays' C and D, as above described, rthen allow the next cornplete pulse to be supplied to the transmitter selected-fory operation. The use of a slow operateislow release' type of relay for relay B will not effect the operation of` the circuit if the circuit shouldv be used inV response to a continuous or steady battery control signaly appearing at:v terminal-,1 in non-multiplex operation.l `Relay BL would merely operate at the time delay brought aboutT by the slow operating nature thereof. The delayed time. of response in no way affects the over-all operation and response of the switching circuit when used with non; multiplex operated telegraph transmitters. However,. as pointedl out above, when the circuit is used to control the operation of multiplex operated telegraphA transmitters, the slow operating andv release actionF ofi. relay B will insure that the switching circuit operating in response to control pulses appearing at terminal 1 will. be in syn, chronism with the multiplex` transmitting. equipment.A Only a control pulse sufcient in` size to insure the ade-l quate and synchronous operation of the-transmitters will be passed from terminal. 1 thru the switching` circuit to the clutch of the particular transmitter under control-.

During the normal operation of artransmitting. station,A it is oft times necessary to transmit messages other than the regular type of` message communication.l For example, it may be necessary to repeat a message or to.' transmit testingsignalsfor the purpose'of checking equip-- ment. During suchtransmission it-is not necessary and,. in fact, is objectionable to have` the numbering trans mitter precede the message with a number. V'l2-he autof matic switching circuit of4 the inventionprovidesmeans for disconnecting the numbering transmitter vfrom the,V circuitV so as to avoid such operationy of the numbering.- transmitter. s v l s K When the operator desires tlc-,forwardapmessage` not preceded by a number, he operatesa controly deviceconnected to terminals 8 and 9 which, for example, may. be a normally open push-button switch 22`. Upon the closing ofv the switch 22, momentarily acircuit is closed. to complete a path from the positive terminal thru-ref sistor R8, terminals. 8V and 9 and resistor R10 tothe windingi of relay D, the other side of. which1 is connected to ground. Relay D- will operate, disengaging Contact 3 and armature 4 of relay D.y Upon. the opening of..

contact 3 and armature 4 of relay D relay C cannot be operated and in fact will. remain` in anfy inoperativef condition regardless of theoperation of4 vthereirl'aining relaysy in the circuit. The opening of. t-hejl contacts of relay D will disconnect the winding of relay C from: the;v

positive terminal of a source of. potential; WhileY the push ,button 22 or other control device connected to terminals 8 and 9 is momentarily closed, one of the transmitters A or B is selected for operation and relay FA or FB is operated by the completion of a ground connection thru terminals 6 or 7. Relays A and B will be operated in the manner described above. Relay C will remain inoperative, relays D and E remaining activated in response to the operation of relays A and B. A control signal which may be a continuous or pulse type signal is connected from terminal 1 to either transmitter A or transmitter B thru terminals 4 or 5, respectively, thus `having avoided the use of the auxiliary transmitter N. Upon the completion of the message, relay FA or FB will be deactivated, depending upon the particular transmitter selected for use, returning the switching circuit to its stand-by condition.

' In order to eliminate arcing across the contacts of the relays, a surge suppressor is connected directly across the winding of each relay, which may, for example, take the form of a pair of crystal diodes 20 and 21 connected as shown in Figure l.

' The particular values of the resistors included in the circuit will be determined in accordance with the particular type of relays and application in which the circuit is to be used. Figures 3 and 4 disclose relays of the multiple contact telephone type, as shown in Figure l, which may be utilized in such a circuit arrangement. Relays FA, FB, A, C, D and E are of the U type, the construction of which is shown in Fig. 4. To assist in an understanding of the operation of the circuit shown in Fig. 1, the particular contacts used in the circuit by each of the relays is shown in Fig. 3. Relay B, which is operated in response to a control signal appearing at terminal 1, is of the Y type shown in Fig. 4. An examination of Fig. 3 will show that relay B utilizes transfer contacts, 1, 2 and 3 and normally closed contacts 8 and 9, the remaining contacts of the relay not being used. It is to be emphasized that the particular relays shown are given merely by way of example. The invention is concerned with a sequential operation of the relays and, therefore, the particular type of relays used as to the make-up of the contacts may be determined in accordance with the equipment available and in accordance with the particular application to which the invention is applied.

In a circuit constructed in accordance with the invention, relay B was a 25 milli-second operating-55 millisecond releasing relay at 60 ma. winding current. It was found that such values for the slow operateslow release relay secured the desired operation. It should be noted however, that relay B does not necessarily have to be a slow operate-slow release type relay, if the relay type chosen for relays A, B, C and E are such that their normal operate times and release times meet both of the following conditions, namely:

(l) The operate time of relay B plus the operate time of relay C plus the release time of relay A plus the release time of relay B when added together shall be equal to or greater than the total possible length of the multiplex control pulse, and

(2) The operate time of relay B plus the operate time of relay E plus the release time of relay A plus the release time of relay B when added together shall be equal to or greater than the total possible length of the multiplex control pulse.

Then, the automatic switching circuit described herein will operate as required in synchronism with the multiplex equipment without the necessity of relay B having slow operate-slow release characteristics. The construction of the automatic switching circuit herein described to meet the two conditions stated above, without the use of a slow operate-slowvrelease type for relay B, would inno way affect the operation of the circuit as described herein. i

` Typical valuesV of the resistors utilized in the circuit 8 given by way of example with a positive potential of volts are as follows:

Having described my invention, I claim:

l. In combination, a transmitter requiring a control signal for enabling the same to transmit, a relay device set to operate and to release following given time delays, a source of control signals, a first switching means responsive to a condition in said transmitter indicating that said transmitter is ready to transmit to connect said device to said source, said device being set to operate upon the reception by said device of a control signal from said source having a duration corresponding to the operate time delay of said device following the connection of said device to said source, and second switching means responsive to the operation of said device and said first switching means to connect said transmitter to said source to apply a control signal from said source to said trans mitter for enabling said transmitter to transmit.

2. In combination, a transmitter requiring a control pulse for enabling the same to transmit, a first relay device set to operate and to release following given time delays, a source of signal energy in the form of a train of control pulses of given duration, a first switching means including at least a second relay device responsive to a condition in said transmitter indicating that said transmitter is ready to transmit to connect said first device to said source, said first device being set to `operate in response to the first control pulse applied to said first device from said source having a duration corresponding to the operate time delay of said first device following the connection of said first device to said source, and a second switching means including additional relay devices responsive to the operation of said first device and said first switching means to connect said transmitter to said source to apply a control pulse of said given duration from said source to said transmitter for enabling said transmitter to transmit.

3. A combination as claimed in claim 2 and wherein said first device is set to operate following a time delay less than the duration of said control pulses and to release following a time delay less than the interval between said control pulses.

4. In combination, first and second transmitters each requiring a control signal for enabling the same to transmit, a relay device set to operate and to release following given time delays, a source of control signals, a first switching means responsive to a condition in said first transmitter indicating that said first transmitter is fready to transmit to connect said relay device to said source, said relay device being set to operate upon the reception by said relay device of a control signal from said source having a given duration corresponding to the operate time delay of said relay device following the connection of said relay device to said source, a second switching means responsive to the operation of said relay device and said rst switching means to connect said second transmitter to said source to apply a control signal from said source to said second transmitter for enabling said second transmitter to transmit, said first and second switching means being arranged vso that the operation of said second switching vmeans/to connectvsaid` second transmitter to said source causes said rst switching means to operate to disconnect said relay device from said source, said relay device upon being disconnected from said source becoming inoperative following the release time delay of said relay device, means included in said second transmitter operative upon the completion of the transmission by said second transmitter to operate said second switching means so as to operate said first switching means to reconnect said relay device to said source, said relay device being reoperated in response to the reception by said relay device of a control signal of said given duration from said source following the reconnection of said relay device to said source, said second switching means being responsive to the reoperation of said relay device and the operation of said first switching means to connect said first transmitter to said source to apply a control signal from said source to said first transmitter to enable said first transmitter to transmit.

5. In combination, first and second transmitters each requiring a control pulse for enabling the same to transmit, a relay device set to operate fand to release following given time delays, a source of signal energy in the form of a train of control pulses, a first switching means includ ing at least a second relay device responsive to a condition in `said first transmitter indicating that said first transmitter is ready to transmit to connect said first relay device to said source, said first relay device being set to operate upon the reception of a first control pulse from said source having a given duration corresponding to the operate time delay of said rst relay device following the connection of said first relay device to said source, a second switching means including additional relay devices responsive to the operation of said first relay device and said first switching means to connect said second transmitter to said source to apply the next complete control pulse following said first control pulse from said source to said second transmitter for enabling said second transmitter to transmit, said first and second switching means being arranged so that the operation of said second switching means to connect said second transmitter to said source causes said first switching means to operate to disconnect said first relay device from said source, said first relay device upon being disconnected from said source becoming inoperative following the release time delay of said first relay device, means included in said second transmitter operative upon the completion of the transmission by said second transmitter to operate said second switching means so as to operate said first switching means to reconnect said first relay device to said source, said rst relay device being reoperated in response to the reception by said first relay device of a further control pulse of said given duration from said source following the reconnection of said first relay device to said source, said second switching means being responsive to the reoperation of said first relay device and the operation of said first switching means to connect said first transmitter to said source to apply the next complete control pulse following said further control pulse from said source to said first transmitter for enabling said first transmitter to transmit.

6. An automatic switching circuit for selectively controlling the operation of a pair of message transmitters and an auxiliary transmitter, each of said transmitters requiring a control pulse for enabling the same to transmit, said circuit comprising a source of signal energy in the form of a train of control pulses, a first relay device set to operate following a time delay less than the duration of said control pulses and to release following a time delay not exceeding the interval between said control pulses, a first switching means including at least a second relay device responsive to a condition in either one of said message transmitters indicating that said one message transmitter is ready to transmit to connect said first relay device to said source, said first relay device being set to operate upon the reception of a first control pulse from said source having a given duration corresponding to the operate time delay of said first relay device following the connection of said first relay device to said source, a second switching means including additional relay devices responsive to the operation of said first relay device and said first switching means to connect said auxiliary transmitter to said source to apply the next complete control pulse following said first control pulse from said source to said auxiliary transmitter for enabling said auxiliary transmitter to transmit, said first and second switching means being arranged so that the operation of said second switching means to connect said auxiliary transmitter to said source causes said first switching means to operate to disconnect said first relay device from said source, said first relay device upon being disconnected from said source becoming inoperative following the release time delay of said first relay device, means included in said auxiliary transmitter operative upon the completion of the transmission by said auxiliary transmitter to operate said second switching means so as to operate said first switching means to reconnect said first relay device to said source, said first relay device being reoperated in response to the reception by said first relay device of a further control pulse of said given duration from said source following the reconnection of said first relay device to said source, said second switching means being responsive to the reoperation of said first relay device and the operation `of said first switching means to connect said one message transmitter to said source to apply the next complete control pulse following said further control pulse from said source to said one message transmitter for enabling said one message transmitter to transmit.

References Cited in the file of this patent UNITED STATES PATENTS 2,317,995 Krum May 4, 1943 2,478,409 Loughlin Aug. 9, 1949 2,667,533 Zenner Ian. 26, 1954 FOREIGN PATENTS 720,863 Great Britain Dec. 29, 1954 153,173 Australia Sept. 11, 1953 

